In the manufacture of electronic substrates, such as printed circuit boards (“PCB”) for example, it is frequently necessary to apply small, precise amounts of viscous fluids, i.e., those with a viscosity greater than 50 centipoise. Such fluids may include adhesives, solder paste, solder flux, solder mask, underfill material, encapsulants, potting compounds, epoxies, die attach pastes, silicones, RTV, or cyanoacrylates, for example.
Automated fluid dispensing systems are often used for dispensing patterns of such viscous fluids onto substrates with a high degree of accuracy, repeatability, and efficiency. As used herein, the term “fluid pattern,” and variations thereof, refers to one or more lines, arcs, dots, combinations thereof, and/or any other configuration of continuously or intermittently dispensed fluid. Traditional fluid dispensing systems include a fluid applicator, also referred to as a dispenser or valve, mounted to a gantry which is movable for positioning the applicator as desired along three mutually orthogonal axes (X, Y, Z) above one or more substrates positioned generally in the horizontal XY plane. The gantry is generally movable with drive mechanisms controlled by a computer system or other controller. A moving conveyor, generally aligned with the X axis of the dispensing system, may be used to sequentially deliver pluralities of substrates to a location generally beneath a fluid dispensing system. The pluralities of substrates are often organized into and carried by carrier trays, such as a JEDEC tray. The dispensing system may then be operated to dispense a pre-programmed pattern of fluid onto the substrates.
To dispense a pattern of fluid onto one or more substrates held in a carrier tray, the controller first determines the location and orientation of the substrates in the horizontally-oriented XY plane in which the substrates generally lie. A camera mounted to the gantry scans the substrates and captures visual images of reference fiducials provided on the top surfaces of each substrate by traveling along a path that moves across the pre-programmed locations of the reference fiducials which are known by the controller. Based on these captured visual images, the controller determines the actual location and orientation of each substrate in the XY plane. A height sensor, also mounted to the gantry, measures the position of each substrate along the vertically-oriented Z axis for determining a proper dispense height at which a dispensing tip of the applicator should be positioned when dispensing onto the substrate. The controller then operates the gantry to move the applicator along the X and Y axes until the applicator is properly positioned in the XY plane over a desired region of a substrate positioned below. The applicator is then lowered along the Z axis until the dispensing tip is at the proper dispensing height, at which point the applicator then dispenses the pre-programmed fluid pattern onto the substrate. Upon completion of dispensing, the applicator is then raised back up along the Z axis and may be repositioned in the XY plane for subsequent dispensing at a new region of the same substrate or of a new substrate.
For increased manufacturing throughput, fluid dispensing systems have been provided with dual fluid applicators for simultaneously dispensing at first and second dispense regions. As used herein, the term “dispense region” refers to a general region or zone at which a fluid pattern is dispensed. For example, “dispense region” may refer to a substrate generally or it may refer to a particular region of a substrate. Accordingly, the phrase “first and second dispense regions,” and variations thereof, may refer to first and second substrates that are physically independent of each other, or alternatively it may refer to first and second distinct regions of a single substrate. For example, a single substrate, such as a panelized substrate, may include a plurality of distinct regions at which fluid is dispensed.
With traditional fluid dispensing systems, a first applicator is positioned and controlled to dispense at a first dispense region, such as a first substrate, while a second applicator is simultaneously positioned and controlled to dispense at a second dispense region, such as a second substrate. On occasion, the first and second substrates may be rotated in the same way in the XY plane of the dispensing system (i.e., “globally rotated”) relative to the X and Y axes. Global rotation of the substrates may occur when the carrier tray in which the substrates are carried is not aligned with the X and Y axes. Traditional dual dispensing methods have included steps for making an automated, one-time positional adjustment of the second applicator relative to the first applicator along the X and Y axes prior to dispensing to thereby enable simultaneous dispensing of identical fluid patterns onto globally rotated first and second substrates.
However, traditional dual dispensing methods have not included automatically repositioning the first and second applicators relative to each other along the X or Y axes while actively dispensing. In other words, traditional dual dispensing systems do not perform active, real-time positional adjustments of the first and second applicators relative to each other in the XY plane while dispensing. Consequently, traditional dual dispensing methods have not accomplished accurate simultaneous dispensing of identical fluid patterns at first and second dispense regions, such as first and second substrates, that are rotated relative to each other in the XY plane (i.e., “locally rotated”). For example, a first rectangular substrate may be aligned parallel with the X and Y axes and a second rectangular substrate may be rotated in the XY plane relative to the X and Y axes. Such local rotation may occur when a substrate is sized smaller than the carrier tray pocket in which it sits, thereby forming one or more gaps between the outer perimeter of the substrate and the inner wall of the pocket. The substrate is thus permitted to rotate within the pocket in the XY plane, and relative to any one or more adjacent substrates. Additionally, local rotation may be present among multiple dispense regions of a single substrate, for example a panelized circuit board. Traditional dual dispensing methods are deficient in actively correcting for such local rotation while dispensing.
Furthermore, traditional dual dispensing methods have not included actively repositioning the first or second applicator relative to each other along the vertical Z axis of the dispensing system while the first and second applicators are dispensing. Accordingly, traditional dual dispensing systems have not accomplished accurate dual dispensing at first and second dispense regions, such as first and second substrates, where the first and second dispense regions are tilted in the XY plane relative to each other, or where one of the dispense regions is uniquely contoured relative to the XY plane, along the Z axis. Thus, dispense regions that are “rotated” relative to each other may lay in a common XY reference plane. In contrast, dispense regions that are “tilted” and/or “contoured” relative to each other do not lie in a common plane, and the dispense regions are uniquely tilted and/or uniquely contoured relative to the XY reference plane, as described in greater detail below in connection with embodiments of the invention (see e.g., FIG. 13A).
In illustration of the discussion above, FIG. 1 shows a carrier tray 10 having a plurality of adjacent pockets 12a, 12b, 12c, and 12d for receiving a corresponding plurality of substrates 14a, 14b, 14c, and 14d. As shown, each substrate 14a-14d may include a corresponding component 16a, 16b, 16c, and 16d mounted thereto. Each pocket 12a-12d has a depth in a direction perpendicular to the XY plane, and is sized and shaped to retain the corresponding substrate 14a-14d in a centered position and in proper orientation relative to a global origin O. FIG. 2 shows a carrier tray 20 in which pockets 22a, 22b, 22c, and 22d are sized slightly larger than their corresponding substrates 24a, 24b, 24c, and 24d held therein, such that gaps are created between the outer perimeter of each substrate A-D and the inner walls of its corresponding pocket 22a-22d. Accordingly, each substrate 24a-24d is permitted to shift and thereby become rotated and/or translated in the XY plane relative to its centered orientation (shown in phantom) and relative to each of the other substrates 24a-24d. 
FIG. 3 shows the carrier tray 20 and substrates 24a-24d of FIG. 2, but where substrate 24b is tilted relative to the XY plane. More specifically, FIG. 3A shows an angular offset between a bottom surface 26 of substrate 24b and a base surface 28 of its pocket 22b, thereby forming a wedge-shaped gap 25. Such tilting may be caused by the presence of a foreign material between the bottom surface 26 and the base surface 28. Alternatively, tilting of a substrate may occur if the substrate is malformed, for example through warping. As discussed above, traditional dual dispensing methods have not accomplished automated, real-time adjustment of applicator positioning while dispensing so as to accurately dispense at first and second dispense regions, such as first and second substrates, that are misaligned in the manners shown in FIGS. 2-3A. Accordingly, there is a need for dual dispensing methods and systems that address such deficiencies.